1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, and a process cartridge and an electrophotographic apparatus each provided with the electrophotographic photosensitive member.
2. Description of the Related Art
The electrophotographic photosensitive member is basically formed of a photosensitive layer on which a latent image is to be formed by charging and exposure, and a support for supporting the photosensitive layer.
At present, a semiconductor laser has been mainly used as a light source in an electrophotographic apparatus. Further, investigations have been conducted on a material sensitive to the laser light having oscillatory wavelength of the semiconductor laser to find applications in a charge-generating material for use in a charge generation layer of the photosensitive member. Of the materials, gallium phthalocyanine which is highly sensitive to the laser light has been preferably used.
In the case where the photosensitive layer is formed directly on the support, stains on a support surface, and the unevenness of a shape and properties, and roughness of the support surface are directly reflected as film-formation roughness of the photosensitive layer. As a result, an image to be obtained may have blank dots, black dots, and image density non-uniformity. Further, in order to ensure the adhesiveness with the support, protect the photosensitive layer from being electrically broken down, and improve the carrier injection property to the photosensitive layer, an intermediate layer is often provided between the support and the photosensitive layer, instead of forming the photosensitive layer directly on the support.
In addition, the advancement of the current electrophotography is remarkable, and there is a demand for a very high technology with respect to the characteristics required in an electrophotographic photosensitive member. For example, process speed is increasing year by year, and there is an increasing demand for charging characteristics, sensitivity, and endurance stability, and the like. In particular, in recent years, there is a demand for an increase in image quality typified by coloring, and half-tone images and solid images typified by photographs are used more instead of monochromic images and images mainly composed of characters due to the coloring. Thus, the image quality thereof is increasing year by year. In particular, in the case of performing an image forming wherein a light-irradiated portion of one output image will become half-tone in the next rotation, an allowable range for a phenomenon in which the density of only a portion irradiated with light will become high (positive ghost phenomenon), or, conversely, for a phenomenon in which the density of the portion irradiated with light will become low (negative ghost phenomenon), is becoming remarkably limited. It is considered that the ghost phenomena are caused as follows. That is, the use of a charge-generating substance with high sensitivity increases the absolute number of carriers, and electrons are liable to remain in the charge generation layer and the intermediate layer, which serves as a memory. This phenomenon is remarkable particularly when a material with high sensitivity such as gallium phthalocyanine is used as the charge-generating substance.
Meanwhile, the reduction in cost and the miniaturization are advancing year by year, and there is an increasing demand for a technology of reduction such as cleanerless and pre-exposureless. In particular, the pre-exposure is not mounted in most cases at present. Thus, the level of ability to suppress a ghost phenomenon of the electrophotographic photosensitive member mounted on the electrophotographic apparatus without pre-exposure needs to be higher by several stages than that of the electrophotographic photosensitive member mounted on the electrophotographic apparatus with pre-exposure.
As a technique of suppressing ghost, an example in which polycyclic quinone, perylene, and the like are contained in an intermediate layer is disclosed (Japanese Patent Application Laid-Open No. 08-146639). Further, an example in which a metallocene compound, an electron-withdrawing compound, and a melamine resin are contained in the intermediate layer is disclosed (Japanese Patent Application Laid-Open No. 10-73942). Further, an example in which metal oxide particles and a silane coupling agent are contained in the intermediate layer is disclosed (Japanese Patent Application Laid-Open No. 08-22136). Further, an example in which metal oxide particles surface-treated with a silane coupling agent are contained in the intermediate layer is disclosed (Japanese Patent Application Laid-Open No. 09-258469). However, these examples do not have sufficient effects at the above-mentioned high ghost level. Further, an example of suppressing image defects such as black dots, using ethylene-acrylic resin in an intermediate layer, is disclosed (Japanese Patent Application Laid-Open Nos. 01-289965 and 02-183265).
Further, the above-mentioned ghost phenomenon is liable to occur particularly in an electrophotographic photosensitive member using an intermediate layer, compared with the case of forming a photosensitive layer directly on a support.